The invention relates to an arrangement for dosing a coal charge to a coking battery and to the utilization of this arrangement in coke plants.
The shortage of raw materials and in particular fossil fuels for generating power in the whole world have pointed to the necessity of applying in coke plants such processes which make it possible to produce blast furnace coke out of low quality coal normally not suitable for coking. As is well-known, there is a shortage of high grade cokable coal on the world markets, a situation which makes such coal relatively expensive. There is a trend in the development of blast furnaces to use hearths of larger and larger diameter requiring charges of coke with sufficiently favorable abrasivity and strength. Such a coke can be prepared from preheated coal having average coking properties. It is, however, equally necessary to satisfy requirements for the maintenance of a healthy ambient working atmosphere in the plant.
The actual state of the art includes several solutions for drying, preheating and dosing of coal charges. These solutions, however, do not meet all the requirements for a continuous operation without breakdowns. The prior art processes utilize a number of mechanical transport means for the preheated charge, including a main hopper and worm conveyors. The operation becomes, by virtue of these arrangements, rather complicated. To wit, breakdowns occur frequently, there are high labor requirements for the attendants, and the useful life of the arrangement is rather low.
In prior art arrangements which are presently in operation, the wet coal is conveyed from a charging hopper to a preheating column by means of a system of worm conveyors, whose speed is adjustable, which are remotely controlled from a control post of the preheater. The wet coal enters a quick-acting drying device where it contacts a stream of hot gas. The gas takes along the partly dried coal into a thinner phase of a fluid bed. A rotating mill is provided in the lower part of the fluid bed which quickly disperses and mixed coal particles in the gas stream and reduces the size of larger coal particles. The final size of coal particles is about 1/4 inch and 90% thereof can pass through a sieve with 1/8 inch mesh. All preheated coal rises and 99% thereof is separated in a cyclone separator, the rest in smaller secondary cyclone separators. Coal, preheated to about 260.degree. C, is conveyed to a distribution container and, by means of feeding means and a conveyor, is passed over to dosing storage bins. The gas is separated into two streams at the output from the secondary cyclone separators. The excess gas passes through a wet scrubber and is released to the atmosphere. The recirculation gas is compressed by a recirculation blower and is returned into the combustion chamber, where it is added in order to cool down the stream of combustion gases passing to the preheater. The required gas speed in the preheating column is obtained by automatic regulation of the recirculation stream of gas. Fine coal particles removed from the outgoing gas in the scrubber are taken away from the circuit of the circulating liquid as foam in a system of flotation containers. The foam is added to the foam from the flotation containers and the whole amount is dried in a vacuum filter. The filtrate is added to the wet coal in the feeding hopper.